Device for arresting undulations in bridging structures



Dec. 28, 1948. M. R. WOLFARD 2,457,426

DEVICES FOR ARRESTING UNDULATIONS IN BRIDGING STRUCTURES Filed Nov. 5, 1945 5Sheets-Sheet 1 ATTORNEY M. R. WOLFARD DEVICES FOR ARRESTING UNDULATIONS Dec. 28, 1948. 2,457,426

IN BRIDGING STRUCTURES Filed Nov 5 1945 3 Sheets-Sheet 2 QN\ MAN A INVENTOR.

BY W NN m, ww q IWPOI. Q w 3 2 m Q Q N $3 Nsbk m I Q Q r. M h w h% .v I v h Y &\ @SN w h m. h /////Z g My AW Wb \ww m@ I v Q,- N N W v v ATTORNEY Dec. 28, 1948.. WOLFARD 2,457,426 DEVICES FOR ARRESTING UNDULATIONS IN BRIDGING STRUCTURES Filed Nov. 5, 1945 3 Sheets-Sheet 3 MerLRQZVol/ard INVENTOR.

BY W

ATTO

Patented Dec. 28, 1948 umrm PATENT errics DEQVIQEEQKiARRESTINGUNDULADIONS mcanmeme srnucrmnns,

MerlR. vWilliam-d, Cambridge, Mass.

Amglication November 5, 1345,,SbriaLNo. 626,66L.

This invention. relates to" devices for arrestin undulations, in a bridging structure.

More particularly the invention-relatesto im provements-in .bridgingstructures in.w hich there is a, principal lengthwise.loadssustaining element having. inflections sucli.that.the, advent. ofg'llve loading tends. to cause. undulation. ofitliatfelement';

It .is an obj ect ofv Itheinventiontoprovide rlde; ing structures, that. areoisliglit. weight, in which the: desired stability is, attained with little. on no additionv of. weights beyond. what; is. required: for the loads that are toobecarriedl The bridging. structures. concerned may,- be bridges of. the suspension .typeaors bridges; of; the truss typeon may. be trusses..of.'otlier sorts and for other: services in. which, WindS,,0I; tram'c.,0r machinery. or. other disturbances tendi to; cause vibrations. Theusuallmat'erials .ion such. 5111110.:- turesare highly. resilienuzeag steeln In the.case

of steel, the elasticity, of steelissuch. tliatlnrac:

tically. all of, the. workdone imd'eflecting ,a.,steel element isjpresentas energy, to movetliatld: flectedi element back. to its initial position; and the momentum. imparted. by; this return move: ment carries .the elementbevondiitssinitiallposition.. If there are repetitive-impulses imhars monic sequence, ,eac'htimpulse .-adds .an ii1crement to, the amplitude of the. undulations.

It is a specific ObjECtlOfabhQiilVfiilfi-Ol'liO,81111831 the. initial. movement. which eaclideflecting; iin: pulse-tends-to produce... Eor. manymracticalnurs poses-itLis,sufilcientvto.arrest only, thosesundulas tions which the smaller defiectingjinplllses tend tovproduce, and to permit; defleotionunder. the impact of large live loads. This,is..permissible because the undulationsbv the heavierloadsere greater, in length, and are slower in: sequence. For example, it has been well; establishedi'that suspension. bridges, which. are entirely adequate Y for resisting disturbance by heavv traflifr, may nevertheless become greatly disturbed; or even destroyed, by relatively. light repetitlverimpulses of higher frequency causediby'windsr.

The prompt and'positive arrestlng ofthe undu: lating; movements that the; smaller forces" tend to produce is sufllcient to prevent theibuildlng -u'p of those" largehigh, frequency amplitudes? of movement" which are objectionable andmay; be=- come destructive: This-positive: arresting: means also restricts" travel of theshorter; l'ligh'er' irequencyundulations-alongthespan:

The invention arrests incipient movememeby providing a dead" load burden. that is sustained in common by two particular regionsof z a: prim cipal load-carrying element? Such a common burdenis available tobe transferredto, and be sustained'bv either, of said: regions, that is, to migrate to one or the: other o f'.'saidfregions, as live loading; tends tocause rise, firstgat'thehone and'tHematithe other. ofjthose regions. One-of these particular regions islocated in each endlialfiofuthespan. The said'icommon burdenmay be, a normaLpart1 of the. structure, or may, be something added'fbr tl'le purpose, In, so .far. as it". becomes released; by either of these, two re-v g ions where it is sustained; in common it' will migrate to the, other. oi"those,reg ions i: e., will be transferredf toand; become sustained at that other:

Theinvention isapplicable in bridging $131110.- turesnfgvarious types. Among the .includedfjtypes arethose in-which a principal ielement'hangswith sag,. and; sustains its loads by tension as the cable. ofoa v suspensionbridge. Andi trusses. are included; in which a. rincipal1 loadrsustainihg element, which; sustains its, load; by compression is. inclined upwardjfiiom. ends..wliich. arer fast to tfieslow-er; chorcLofItHe truss, themiddle portion of: ti'iis. element. being ap roximately horizontal. Preferably the; inclination. ofthese, endrportions isless than ,45'fr.om.theJiorizontal;

The. accompanying; drawings. show embodiments of. the invention, diagr.ammatically;.. In them;

Figure Lise-sideoelevation illustrating a, simple brid e. 0Il $I1lCti0n;,ShO.Win& on y a. mainJoadlsustaining, element; andlmigratory; loading means coactiilg, therewith;

Fi ure 2.;is. an. end .elevationsof themain. load: sustaining elementl oi, Figure- 1;. in crossv section at; 2"-'2,.er1la1'g. d,

Figure 3; a. side, elevation of apparatus, for illustiatinggthe principle of. migration of, loading, asxit may be applied to, the arrestingofj vertical movements;v

Fl gure i is a side elevation ofqa truss which has: two panel-loaded'pointsconnected for migration ofloading;

Figures 5; 6'-and"7 are greatly enlarged'details of' partsgofFi'gure 4; ,in which Figure 5' is anend elevationxinsection on; the line 5-5f; Figure 6, a" side-elevation of the: region .of inflection of the grincipal load carrying element; and Figure 7' is a side elevation at'tlie connection of the com pressionelement to the tension element, in me: dial section Figure -8 *is a side elevation :of' a six' panel truss; having threepanel-loaded points; connected for migration or loading FigureQ is'a sideelevation' ofa" ten panel truss;

I in which there are three panel-loaded points for migration of loading, and the inclined parts of the principal load-sustaining element are supported by struts at their mid-portions;

Figure is a side elevation of a truss having two panel-loaded points connected for migration of loading, like Figure 4, with an extension of 1 two panels at each end;

sion of two panels is added at each end; and H Figure 12 is a side elevation of a truss having a mid-portion arrangement similarto thato f"- 3 Figure 11, but having its end extension panelsof conventional type.

In the accompanying drawings,

the pivots of clevises 35, 36 through which tension elements 3?, 38 pass for loading the ends of the'beam. Eachtension element has its outer end fast to the horizontal support 30, beyond the iend of the beam'34; has its middle portion passing through the clevis or 3B; and has its inner end beneath the pivot 32, fast to the freeinner end of a radius bar 40 whose pivot M is at a horizontal distance on the support 30'so that these inner ends of the tension elements '31, 38

can moveup or down, but cannot move lengthwise of the horizontal support. A weight 42 hangs on that free end of the bar, and so constitutes a dead load which is a burden that is common to these two tension elements and is imposed ,by them on their several clevises 35, 36.

Thus, each limb of each. tension element 31, 38v applies to its respective clevis'35, 36 a loading whose vertical downward component equals half of the weight 42; the total downward vertical loading at the clevis 35 is equalto the weight 42; the total vertical downward loading atv the clevis 35 is equal to the same; and'the beam 34 is balanced. Inasmuch as the loadings at clevises 35 and 3 6 are produced by a burden Which they sustainv in common, any part of that common burden which one of these clevises ceases to sustain becomes imposed on theother clevis.

These being in balance, the adding at 35, of

a loading such as would start a down swing of V that the weight 42 is one pound, so that there is initially one pound of dead load at eachclevis, and that the apparatus is in a state of balance, and assuming further that an added load of one pound becomes incident at 35, simulating the advent of a live loading on an end portionof a bridge, then one-half pound of dead loading mi? grates from 35 to 33, and produces a fresh balance of loading, viz., one and one-half pounds at each point 36 and 35. The fact that the dead load 42 issustained incommonat; 35 and 35 1.

Figure 3 represents illustrative balance 'beam apparatus *in* which the arresting of vertical movement, is.ac-; complished by migration of loading. The element 36 is a horizontal support on which two struts 1 3| stand as an inverted V supporting a pivot 32 :at the mid-pointof the beam 34, this pivot 32 corresponding to the. knife-edge of a balance. iEquidistant, at opposite endsof the beam, are

4 promptly and positively arrests that rise of the end 36 of the beam, and that fall of the end 35 of the beam, which the weight added at 35 otherwise would cause.

The total dead load that is carried by both at 35 and 36 is available to migrate to either 35 or 36. That is, the total dead loading that was originally carried at both regions 35, 36, can be imposed ateither ofthem.

For anotheriexample assume as before that the weight'42 one pound, and that the apparatus is in balance, and that an added weight of two pounds becomes incident at 35. Then a new balanoe-isreached as the whole of the initial loadingof one pound that was at 35 migrates to 36,

mal ing the beam 34 be in balance with two pounds of loading at each end 35, 36.

' If this two "pounds of live load added at 35 should become transferred to the other end 33 of the beam, as when a traflic load movesacross abridge, thenthe total of dead load which is available for migration, two pounds, migrates back from 35150135 and arrests movement of the beam at'the incipience of its fall at 35 and of its rise at 35. This 'persistenceofthe beam in balance continues so long as no magnitude of a loading added at 35 or at 35 exceeds the capacity of the apparatus, which,under the assumed conditionsof the numerical example, reaches its limit with' an added loading o'f two pounds at either end of the beam. If either end suffers incidence of more than two pounds added loading there will be movement of the beam.

Figure 1 illustrates how the invention may be applied in a bridge of" simple construction, as, for crossing a, ravine, in which the migratory loading means can be located under a mid-portion of 'the span. The principal load sustaining element IO'has each of its ends l2 held at a fixed level and held against lengthwise movement. It is subjectto migratory loading at each of two regions," [8 arid 28, which are at approximately equal distances from'the center of the span, at which regions there are pulleys over which the loading. cables M,24 pass from their anchorages 13,23, beneath their respective end portions of the bridge, to. a lever "26 whose fulcrum 22 is secured at a convenient 'place beneath the bridge. The lever is powered by a weight 20, and has its work arm in two branches I5, 25 which respectively are connectedto the cables I4, 24 forloading in common two'pa'rticular regions of the principal load sustaining. .element II), by transfer through the pulleyconnections l9"from the pulleys I8, 28.

Tautness'of these cables l-4,'24 can be adjusted byanyfsuitable means, as turnbuckles 2|.

The imposing of'burden at the regions indicated'in each endj-half-portion of the span, when the structureis static, applies at each such region ajmagnitu'de of dead load burden which exceeds that dead loa'd burden which is imposed at any other regionof equal extent in the same encl half-portion of the principal sustaining element.

The cables/I4, 24 beingJequal in stress, when thefstructure is static, an advent of live loading on the. element Ill at'a region I8 or 28 will produce. migration of loading between these regions l8, 28. This migration isof dead load burden im- 1 posedon :those'regions in common by the lever 26 and'cables I4, 24 in the manner explained above for migration between the points 35, 36 of Figure 3. I

" Most favorable results are-obtained when the two regions I8, .28 of Figure 1, are located at @99 3 equal .dista s i omes n m t span.

cameras and are about four-tenths =of the length of ithe span apart. However, -benefits are had n they are located anywhere within the range of twotenths to six-tenths of the lengthnf 'the span apart.

Figure 1 exemplifies'how the invention may be applied to a. load-sustaining element of abridg- -ingstructure which 'hangs with sag betweensupports. The element ll) sustains 'load' 'by tension, as'the cables "do' in'a suspension bridgeoi customar-y type. This element,and theeables, tend to=rise ln=one end -half-portion whenz'aitraiflc load "comes upon the other end-hali-portion oi "the span. The"invention is likewiseeffective in dealing with aeroedynam'ic disturbances, in which wind impulses may tend'tolift one region of the bridge more than another.

Figure 2 shows the -'principal load sustaining element l'fl having a cross-section in the dorm of an'invertedT, in which the vertical stem of'the T contributes stiffness .to the structure. This is an advantageous distribution of material because, the main loading'is sustained by tension'between the end supports, at least in I the mid-portion of the sparr and this tension is in the lower flange of the 'T.

m the application of migratory loading illustrated in Figures 1- and 3 the common dead load burdenis'a'dded to the s'tructure which is to be stabilized. However the commonload burden for migratoryloading maybe provided "by a part or thestructure which is being stabilized, as, for example, by parts of the platform and its appurtenances.

The structures oi'Figures 4, 8 and 9,'have some features of ordinary trusses have the general appearance of ordinary trusses, and are herein called -trusses,=butthey differ from 'the usual truss in that'thestructure isarranged to provide dead load burden sustained 'in part at each of two particular regions o'f a principal load sustaining element, so that the major portion -of that sustained load is available to migrate to either of said particular regions upon'the advent -of liveloadings whichten'd to cause rise "first at each end-half-portion of the span-it has'an inflection-at a. point where there-is a tendency to risewhen a loadis'applied at-the' similar point in theiother end-haIf-portion; and'these points are the particular regions-atwhicha burden ofdead load is sustained in common, for migration of dead load 'to either region to prevent its rise, so 'to-stabilize the span.

Figure 4 shows :an applicationof migration of loading in simple form, in a truss having five panelslin which'the middle two of :the'four interm'ediate panel-loaded points are connected for migration ofloadlng. The load .which .iscavailable "to'migrate is "those parts of the platform and-its appurtenances whichare hung at those panel loaded points.

Theprincipal load-sustaining compression ele :ment 50 rises, attan inclinatiom from the tenslon other "end incline.

causedby that are inconsequential.

chord i 52 :at one end ofithe-span its .anzinflection point 55, whence it extends approximately 'horizontally to the other inflection Lpoint :56, and thence. it inclines downward ito the tension :chord teatime other v end .of the span. The .fdlstancemi the :poixits155, 15B irom each :o'therzis -preferably within the range of .twn tenths :to six-ttenths [of the 'l'ength of the span. iThe-spanis considered to extend between the :points where .the compression :element 50 .is secured to the tension element :52. This element 50, which may :be a rchannehbarwithithechannel. downward, :has'each OE-its ends heldaagainst-lengthwise slipsrelative'to :theit'ension 'chord 5'2. This holding:may be accomplishedin any convenient manner, an illustrativezmethod :being shown Lin Figure 17 wherein a saddl'e'piece BI secured to the lower 1 chord i2 has ai.notch 53,iinto which the web of-the iohannel fits, to :sustain endwise thrust :and vertical load. The channel banis'shownias havingits flanges out away-iatiits points ofiinflectmn 5d, 58, asiindicated in Figure B-ati54, and the web is -bent 'to i iorm' the -inflection. In a channel bar lthus arranged and loaded, the compression load applied'rto the web between the fiangesitends 'to bend the :bar downwardtbe-tween 'thoselload'ed points. The weight of the bar also'tends to bend the bar downward. These two tendencies are suflicientrtoassure that 'the middle of thiselernentwill never be deflected itoiabove'fthel horizontal by any vibrating tendency. The making ='o'f this inonprismati'c section thus contributes testability. Figure 5 shows how a :tie, as :12, may be conveniently pivoted between the flanges of achannel :bar 'element 51!. The element "54! is not necessarily one continuous piece; iit may 'be of joined piecesyandthese'may .be oonn'ected at the points of inflection by pivots or otherwise. This element 50 functions as a single: element; it is convenientlyhere 'so tre'ate'd. In Figure l'the'dead load-of abridge platformis 'repr'esented a's being-separate weights 58 hung frompanehloaded points 60, '54, and 10. The panel-loaded point BI] has ties-'6l,-"'62respectively connecting it to the inflection-pointsiS, 56. The panel-loaded point '10 is connected by ties 1 I, *12 respectivelyto 'the "same two inflection points 5 56, '55. By this arrangement the dead loads *which are -at thepanelloaded points'fifl and"lj0-'aresustained in common I at the inflection points 55, *56. Therefore these loads constitute a 'common'burden which is available to migrate to whichever point 55, '56 tends to rise upon advent of live loading.

"A tie d5 'c'onnects'the inflection region55 to'the panel-loaded point =64 which 'is'under thea'djacent inclined part of the compression element; 'an'd similarly tie69 connects'the-other inflection region56 to the panel-loaded point 68 under the Preferablythe inclined end portions of the element 50 are set at an angleless than from the horizontal, and in consequence the vertical 'component' of anyrotative movement about the held end of the element exceeds-the horizontal component of the same movement which islengthwise of'thespan. This minimizes "longitudinal movement of the upper part of the 'truss; and the vertical arresting actionof the migration of loading is so positive in'casesof ordinary tralfic that all-movements which maybe In cases of extraordinary overloading, as when a military tarlk passes over ahigh-way bridge, the invention permits the loa'ding to deflect the element 50,

without damage.

1 Figure '8 is *similar to Figure 4 in "the general I01; and III, H2.

tion point. 3 clined part of the compression element I20 there is a strut IZ'I approximately normal thereto and extending to a panel-loaded point in the lower which the element 50 terminates. a truss in which there are eight panel-loaded arrangement of the compression element 80 and loaded points 94, 98. It differs in that there are three panel-loaded points I00, I05, IIU connected for migration of their loading to the two inflection points 85, 85 respectively by ties IUI, I02; I06,

It difiers also in that the compression element 80, between its inflection points I 85, 86 is set with a slight bend which keepsits 1 lower chord '82, which correspond to 50 and 52 in Figure 4; the inflection points 85, 86, which I correspond to 55, 56; and the ties 95, 99, which 1 correspond to the ties 65, 59, and run to the panelmid-portion below the horizontal level of those 1 points; and that a strut 81 extends downward from the element 86 at that bend to the panel- This is'in contrast to the usual That loaded point I05. practice of elevating the center of a truss.

tends to instability, but in this construction an},

tendency of the mid-portion of the element to I move is in the direction in which the migratory ten panel-loaded points of which three, I30, I35 I and I40, are connected for migration of loading to its points of inflection I25, I26. The other panels may be supported in any suitable way, that which is illustrated being by ties from the inflec- From the mid-portion of each inchord; and there is an inclined tie to the lower chord between this strut and the end of the chord.

Figures 10, 11 and 12 show arrangements by which the structures in Figures land 8 can be utilized in trusses having a greater number of panels. In such cases the supporting means, at

l the ends of the span in which the stabilizing structure of the invention is embodied, may each be at a distance from the pier that supports its end of the full span of the bridge. That is, the

I82 of the truss.

, In Figure 10 a nine panel truss embodies the structure of Figure 4 in its mid-portion. The

horizontal portion of the compression element 50 has extensions I5I at each end, beyond which are inclined extensions I53. From the junction of the horizontal and inclined parts of these extensions, at each end of the truss, ties incline downward to panel-loaded points, in the tension chord, one of these reaching the panel-loading point at This provides points, only two of which are connected for mi- Igration of loading.

In Figure 11 a ten panel truss embodies in its of the compressionelement, at each end of the truss, ties incline downward to panel-loaded points in the tension chord, one of these reaching the panel-loaded point at which the element 80 terminates.

1 FfigurelZ embodies the structure of Figure 8 in its mid-portion and shows how extensionsat each end can be made by adding panels of usual truss type, two of such panels being shown so added.

In Figures 10, 11 and 12, having this greater number of panels, the common dead load burden that is available to migrate is a smaller proportion of the total dead loadof the platform than is available in the trusses of Figures 4 and 8. Nevertheless the dead load burden imposed on the points of inflection of members 50 or exceeds the dead load burden which is imposed at any other region of equal extent along said members of the truss, in the same end-half-portion of the span; and the stabilization thus provided will be satisfactory for many purposes. I

In thestructures thus described, themanner of stabilization, and its quality, prevent the building upof excessive movements, and so provide a structure in which little strength of the principal I load sustaining elements need be provided much beyond that which is required merely to sustain the'live loads. I

By reason of the prompt arresting of undulations at their incipience, and by reason of the greater flexibility of the structure under extreme loading, the maximum stresses which any given live loading imposes on the main load sustaining elements are greatly reduced, as compared with usual bridging structures. Therefore a lower factor of safety may be used, permitting a bridge to be safe when made with less weight and less cost of material. The greatly reduced possibility of longitudinal movement of the upper part of a truss structure permits the making of that upper part lighter; and the factthat it is lighter makes .its holding more secure," so that another decrement of weight becomes possible.

It is intended that the appended claims shall have expressions suitable for the patent to cover whatever of patentable invention is'herein disclosed relative to stabilizing of bridging structures by loading, in common, regions in opposite end portions of the span for migration of dead loading from one end-half -portion of the span of the structure to the other to arrestrise in'that other.

This is a continuation in part of mycop'ending application Serial No. 435,686, now Patent No. 2,413,019 issued December 24, 1946, which is now limited to bridging structures which are stabilized by migration of loading upward and downward between regions that arein the same endhalfportion of the span.

I claim as .my invention:

1. A structure having migratory loading means for arresting its own undulations-being a bridging structure, extending between supporting means and sustaining dead load and live load along the span between those supporting means, of atype in which there is a'principal lengthwise element which is inflectedv so that-an incipient depressing of that element inone. endhalf-portion of the span below its static position tends to cause rise of that element in the other end-half-portion of the span, and so that the said principal element extends from a said supporting means at an angle of less than 45 with the horizontalsaid arresting means comprising a distribution of dead load relative to two particular-regions of the said principal lengthwise element, each of which regions sustains a magnitude, of dead load burden which exceeds that imposed on any other portion of equal extent along that element in the same end-half- -po'rtion.of the span when the structure is static;

each end-half-portion of the span having one of these particular regions, they being spaced apart a distance which is in the range of twotenths to six-tenths of the length of the span between said supporting means; there being tying means extending from a common dead load burden directly to each of said regions, this common burden being sustained in part at each said region when the structure is static, and said part constituting a portion of the said greater magnitude of dead load burden at a said region; at least a major portion of the said common burden, so sustained in common, being available to migrate through the tying means to either of said regions, upon the advent of live loadings which tend to cause rise first at one of said regions and then at the other of these said regions.

2. A structure having migratory loading means for arresting its own undulations as in claim 1, in which the said principal lengthwise loadcarrying element is one that hangs with sag between said supporting means, has anchorage connections at its ends; and in the span sustains loading by tension pull on said connections.

3. A structure having migratory loading means for arresting its own undulations, as in claim 1, being a truss in which the said principal lengthwise element is a compression element having an approximately horizontal middle portion between points of inflection from which its end portions incline downward to the tension chord of the truss at a said supporting means and are there held against lengthwise slip relative to that tension chord; the said particular regions being at these points of inflection in said compression element.

4. A structure having migratory loading means for arresting its own undulations, as in claim 3; further characterized in that said tying means include, for each said region, a plurality of ties pitching inward and downward from that region to points which severally sustain panel dead load; a plurality of panel-loaded points being each thus tied to both of said regions to impose on those regions in common the load which is sustained at the plurality of said panel-loaded points.

5. A structure having migratory loading means for arresting its own undulations, as in claim 3; further characterized in that said tying means include, for each said region, a plurality of ties pitching inward and downward from that region to points which severally sustain panel dead load; a plurality of panel-loaded points being each thus tied to both of said regions to impose on those regions in common the load which is sustained at the plurality of said panel-loaded points; the said approximately horizontal portion of the compression element having its midportion set at a level slightly below the straight line between its points of inflection; and there being a strut extending downward from that mid-portion to a said panel-loaded point at the tension chord.

6. A structure having migratory loading means for arresting its own undulations, as in claim 3; further characterized in that said tying means include, for each said region, a plurality of ties pitching inward and downward from that region to points which severally sustain panel dead load; a plurality of panel-loaded points being each thus tied to both of said regions to impose on those regions in common the load which is sustained at the plurality of said panel-loaded points; there being also at each said region a tie pitching outward and downward to a panelloaded point beneath the respective inclined said end-portion.

7. A structure having migratory loading means for arresting its oWn undulations, as in claim 3; further characterized in that said tying means include, for each said region, a plurality of ties pitching inward and downward from that region to points which severally sustain panel dead load; a plurality of panel-loaded points being each thus tied to both of said regions to impose on those regions in common the load which is sustained at the plurality of said panel-loaded points; there being also at each said region a tie pitching outward and downward to a panelloaded point beneath the respective said inclined end portion; a strut rising from the last mentioned panel-loaded point to a mid-portion of the said inclined end portion; and a tie from the joinder of this strut and end portion, pitching downward and outward to another panelloaded point.

MERL R. WOLFARD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

